A machine for making flat-bottom two-piece containers of paper and paper-like materials usually has a turret which is stepwise rotatable about a vertical turret axis and which comprises a number of mandrels that have their axes radial to the turret axis and disposed at uniform angles around it. Stepwise rotation of the turret brings every mandrel to each in turn of a succession of stations that are space around the mandrel orbit.
Each mandrel has a flat face at its end remote from the turret axis and tapers along its length to that face. At one of the stations to which the mandrel is brought, a bottom blank for a container to be formed is applied flatwise to the end face of the mandrel and held in place there by suction inlets in that face. A side blank is then wrapped snugly around the mandrel to bring its opposite side edge portions into overlapping relationship, and those overlapped portions are clamped against the mandrel and thus bonded to one another to form a side seam.
To provide for formation of a bottom seam at which the side blank is sealed to the bottom blank, the bottom blank has a peripheral flange that projects away from the turret axis and the side blank is wrapped around the mandrel in a position to project beyond the end face of the mandrel and surround the flange. The flange and its contiguous portion of the side blank thus comprise a bottom rim on the container. Usually the side blank initially projects a substantial distance beyond the flange on the bottom blank, and the machine has a station at which this projecting portion of the side blank is rolled radially inwardly and back over the flange to bring the bottom rim to a condition in which the flange is sandwiched between portions of the side blank. The mandrel is then swung to a bottom expander station at which the sandwiched layers of the bottom rim are clamped into tight engagement with one another so that thermoplastic coating on the blanks, previously heated to its molten state, can bond those layers to a liquid-tight bottom seam for the container.
The bottom expander conventionally comprises a shuttle that is movable back and forth in directions parallel to the axis of a mandrel that has been brought to the bottom expanding station. As the mandrel is moving into that station, the shuttle is in a rearward retracted position at which the bottom expander is clear of the mandrel and the container blanks on it. When turret rotation stops, the shuttle moves forward to carry bottom expander tooling thereon into operative relationship to the bottom rim of the container on the turret.
The bottom expander tooling comprises an outer tool which is fixed to the shuttle and which is in the form of a ring that surrounds the bottom rim of the container, and inner tooling which is movable relative to the shuttle to clamp the layers of the bottom rim against the ring. For a container having a non-circular bottom, the inner tooling comprises a plurality of plate-like tool elements that are actuated by a driver which moves back and forth along an axis in the shuttle. The several tool elements are disposed in a common plane that is normal to the driver axis, and each has a radially outer edge surface that is configured for clamping cooperation with a portion of the ring. The front end portion of the driver is formed as a substantially pyramidal head with forwardly convergent driving surfaces, and each tool element is fixed to a carrier that has an oblique driven surface which so complements and cooperates with one of the driving surfaces on the driver head that forward movement of the driver wedgingly propels the tool elements radially outwardly for their clamping cooperation with the ring.
In prior bottom expanders for noncircular containers, the tool element carriers were confined to radial in and out movements by cooperating sliding guide surfaces on them and on the shuttle, and they were biased radially inwardly towards their normal positions by coiled compression springs reacting between them and the shuttle. The guide surfaces had to be very accurately machined so that they would confine the tool elements to radial in and out motion and against play in other directions while nevertheless providing clearances adequate to prevent binding. Notwithstanding the precision that had to be maintained in these guide surfaces, they were subjected to severe pounding during operation of the bottom expander because the driver moves forward at high speed, and its oblique driving surfaces therefore impose large forward forces upon the tool element carriers. As a result, the guiding surfaces soon became worn, and the tool element carriers had to be replaced frequently. This was expensive, not only in down time on the machine but in the cost of each replacement carrier itself, inasmuch as the carrier was a precision-made part of complicated shape.